Fluid control device

ABSTRACT

In a fluid control device, a valve body is prevented from being pressed forcefully against a valve seat or the like, and an excessive load is prevented from acting on a motor. A flow rate adjustment device includes a first engagement portion, and a second engagement portion that is capable of moving relative to the first engagement portion and transmitting and receiving rotary force. The flow rate adjustment device includes a valve body that adjusts an opening of a flow passage, and a rod that is coupled to the valve body. The flow rate adjustment device further includes a male screw portion and a female screw portion that are intermeshed so as to be fed relative to each other in the axial direction, a projecting portion that restricts movement of the second engagement portion, and a first cylinder that restricts movement of the rod.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fluid control device that controls aposition of a valve body on the basis of rotation of a motor.

2. Description of the Related Art

In a conventional fluid control device of this type, a position of thevalve body in an open condition is determined by rotating a male screwmember coupled to a drive shaft of the motor such that a female screwmember meshed to the male screw member is fed in an axial direction ofthe male screw member (see Patent Documents 1 and 2, for example). Inthe devices described in Patent Documents 1 and 2, a stop position ofthe valve body in the open condition is determined when a piston coupledto the valve body impinges on the female screw member.

-   Patent Document 1: Japanese Patent Application Publication No.    2003-083466-   Patent Document 2: Japanese Patent Application Publication No.    2007-278514

Incidentally, with the devices described in Patent Documents 1 and 2,the female screw member may impinge on the piston or another member whenan opening of the valve body in the open condition is reduced by feedingthe female screw member in the axial direction of the male screw member.In this case, the valve body may be pressed forcefully against a valveseat or the like, and an excessive load may be exerted on the motor whenfeeding of the female screw member is restricted.

BRIEF DESCRIPTION OF THE INVENTION

The present invention has been designed in consideration of thesecircumstances, and a main object thereof is to prevent a valve body frombeing pressed forcefully against a valve seat or the like and anexcessive load from being exerted on a motor in a fluid control device.

To solve the problem described above, the present invention employsfollowing means.

First means is a fluid control device including: a motor having a driveshaft; a first engagement portion provided on the drive shaft; a secondengagement portion configured to move relative to the first engagementportion in an axial direction of the drive shaft and receive a rotaryforce from the first engagement portion. A valve main body has a flowpassage for a fluid and a valve seat portion; a valve body is providedto face the valve seat portion in order to adjust an opening of the flowpassage. A moving member is coupled to the valve body of which movementin the axial direction is permitted and of which rotation about thedrive shaft is restricted. An elastic member is configured to exert aforce on the moving member in a direction for causing the valve body toapproach the valve seat portion. A first restricting portion isconfigured to restrict movement of the second engagement portion to theside of the valve seat portion beyond a first restriction position. Anda second restricting portion is configured to restrict movement of themoving member to the side of the valve seat portion beyond a secondrestricting position. The second engagement portion and the movingmember are screwed together such that the second engagement portion andthe moving member move relative to each other in the axial directionwhen rotated relative to each other.

According to the configuration described above, the first engagementportion provided on the drive shaft of the motor is rotated by drivingthe motor. Rotary force is transmitted from the first engagement portionto the second engagement portion, and as a result, the second engagementportion is rotated. Further, the flow passage for the fluid and thevalve seat portion are provided in the valve main body, and the valvebody for adjusting the opening of the flow passage is provided to facethe valve seat portion. The moving member is coupled to the valve bodysuch that movement thereof in the axial direction of the drive shaft ispermitted but rotation thereof about the axis is restricted.

The male screw portion and the female screw portion are provided oneither the second engagement portion or the moving member, respectively.The male screw portion and the female screw portion are meshed to eachother so as to be fed relative to each other in the axial direction ofthe drive shaft when rotated relative to each other. When the secondengagement portion is rotated, therefore, the moving member that isrestricted to rotate and the second engagement portion rotate relativeto each other.

At this time, movement of the second engagement portion to the valveseat portion side beyond the first restriction position is restricted bythe first restricting portion. Therefore, when the drive shaft isrotated in a direction for causing the second engagement portion and themoving member to approach each other, or in other words a direction forpressing the second engagement portion against the first restrictingportion, the moving member is fed in a direction separating away fromthe valve seat portion. Force is exerted on the moving member by theelastic member in a direction for causing the valve body to approach thevalve seat portion. Hence, when the moving member is fed, the movingmember is moved against the force of the elastic member. A distancebetween the valve seat portion and the valve body, or in other words theopening of the flow passage, is adjusted in accordance with an amount bywhich the moving member is fed.

When the drive shaft is rotated in a direction for causing the secondengagement portion and the moving member to head away from each other,on the other hand, the moving member is fed in a direction approachingthe valve seat portion. At this time, force is exerted on the movingmember by the elastic member in a direction for causing the valve bodyto approach the valve seat portion. And therefore the second engagementportion is pressed against the first restricting portion via the malescrew portion and the female screw portion that are intermeshed eachother. When the moving member reaches the second restriction position,movement of the moving member to the valve seat portion side isrestricted by the second restricting portion.

Here, the first engagement portion and the second engagement portion arecapable of relative movement in the axial direction of the drive shaft.Therefore, by rotating the second engagement portion when movement ofthe moving member is restricted, the second engagement portion is fed ina direction separating away from the moving member, or in other words adirection separating away from the first restricting portion. Hence,even when the motor is driven further in a condition in which movementof the moving member is restricted, situations in which the valve bodyis pressed forcefully against the valve seat portion or an excessiveload is exerted on the motor can be suppressed. As a result, particlegeneration from the valve body and the valve seat portion, deformationof and damage to the valve body and the valve seat portion, damage tothe motor, or the like can be suppressed.

Further, the first engagement portion and the second engagement portionare capable of transmitting rotary force to each other and capable ofmoving relative to each other in the axial direction of the drive shaft.Therefore, a reaction to the force for feeding the moving member in theaxial direction and a reaction to the force for feeding the secondengagement portion in the direction separating away from the firstrestricting portion can be prevented from acting on the drive shaft ofthe motor in the axial direction. As a result, an increase in a rotaryload of the motor can be suppressed, whereby a reduction in a durabilityof the motor and an increase in a size of the motor can be suppressed.

In second means pertaining to the first aspect of the invention, thesecond restricting portion is provided with a spacer for adjusting thesecond restriction position, and in a condition where movement of themoving member is restricted by the second restricting portion, a gap isformed between the valve seat portion and the valve body.

According to the above configuration, the second restriction position isadjusted by the spacer in the second restricting portion for restrictingmovement of the moving member to the valve seat portion side beyond thesecond restriction position. Therefore, the gap between the valve seatportion and the valve body, or in other words a flow condition of thefluid, in a condition of maximum closeness between the valve body andthe valve seat portion can be controlled precisely. Further, in thecondition where movement of the moving member is restricted by thesecond restricting portion, the gap is formed between the valve seatportion and the valve body, and therefore the valve body can beprevented from impinging on the valve seat portion. As a result, asituation in which particles are generated from the valve body and thevalve seat portion can be suppressed effectively. The aboveconfiguration is particularly effective when applied to a flow rateadjustment device or a pressure adjustment device used in a conditionwhere the valve body keeps the opening of the flow passage constant.

In third means pertaining to the second aspect of the invention, acylinder configured to guide movement of the moving member in the axialdirection is further provided, and an insertion port into which thespacer is inserted from outside is formed in the cylinder.

According to the above configuration, movement of the moving member inthe axial direction is guided by the cylinder. Further, the spacer canbe inserted through the insertion port from the outside of the cylinder.Therefore, the gap between the valve seat portion and the valve body canbe adjusted finely by the spacer after assembling the fluid controldevice. Hence, a high degree of dimensional precision is not required inthe valve main body, the cylinder, the moving member, or the like, andas a result, fluid control precision can be maintained while suppressingcosts.

In fourth means pertaining to any of the first to third aspects of theinventions, one of the first engagement portion and the secondengagement portion includes a rectangular parallelepiped-shapedinsertion portion, the other of the first engagement portion and thesecond engagement portion includes a recessed portion into which theinsertion portion is inserted in the axial direction, and outsidesurfaces of the insertion portion and inside surfaces of the recessedportion are mutually parallel and fitted together with a gap between thesurfaces.

According to the above configuration, the rectangularparallelepiped-shaped insertion portion provided on one of the firstengagement portion and the second engagement portion can be insertedinto the recessed portion provided in the other in the axial directionof the drive shaft. Further, the mutually parallel outside surfaces ofthe insertion portion and the inside surfaces of the recessed portionare fitted together with a gap therebetween. Hence, the first engagementportion and the second engagement portion can be made capable ofrelative movement in the axial direction of the drive shaft, and rotaryforce can be transmitted between the first engagement portion and thesecond engagement portion. The first engagement portion and the secondengagement portion can therefore be realized by a simple configuration.

Moreover, by exposing the second engagement portion and rotating thesecond engagement portion by hand, the position of the valve body can beadjusted manually. As a result, a maintainability of the fluid controldevice can be improved.

When the motor is constituted by a stepping motor that rotates insynchronization with pulse power, as in fifth means pertaining to any ofthe first to fourth aspects of the inventions, an excessive load can beprevented from acting on the motor, and as a result, the stepping motorcan be prevented from losing steps. Hence, a stepping motor thatexhibits superior position adjustment precision and controllability canbe employed while suppressing a reduction in the position adjustmentprecision due to loss of steps.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial sectional view showing a flow rate adjustmentdevice;

FIG. 2 is a partially enlarged view of FIG. 1;

FIGS. 3A and 3B are a view showing an insertion port and a shim;

FIG. 4 is an exploded perspective view showing a first engagementportion and a second engagement portion;

FIG. 5 is a partially enlarged view showing a valve body openingoperation performed in the flow rate adjustment device; and

FIG. 6 is a partially enlarged view showing a valve body closingoperation performed in the flow rate adjustment device.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

An embodiment will be described below with reference to the drawings. Inthis embodiment, the present invention is realized as a flow rateadjustment device that adjusts a flow rate of a fluid in a semiconductormanufacturing apparatus or the like.

FIG. 1 is a partial sectional view showing a flow rate adjustment device10. The flow rate adjustment device 10 (fluid control device) includes avalve main body 20, a first cylinder 30, a second cylinder 50, a motor110, and a housing 120.

The valve main body 20 is provided with an inflow port 25 through whicha fluid (a liquid) flows in, and an outflow port 26 through which thefluid flows out. The valve main body 20 is formed of achemical-resistant fluorine resin, for example PTFE (Poly Tetra FluoroEthylene). A flow passage 21 connected to the inflow port 25, a flowpassage 23 connected to the outflow port 26, and a valve chamber 22 thatconnects the flow passages 21 and 23 are formed in an interior of thevalve main body 20. The valve chamber 22 is formed as a columnar spacethat opens onto a surface (an upper surface) of the valve main body 20.The fluid flows in at a predetermined pressure through the inflow port25.

The first cylinder 30 is fixed to the valve main body 20 on the opensurface (the upper surface) of the valve chamber 22. The first cylinder30 is formed of a general purpose resin, for example PP (PolyPropylene). A columnar first housing portion 31 is formed in an interiorof the first cylinder 30. The first housing portion 31 penetrates thefirst cylinder 30, and a central axis of the valve chamber 22 matches acentral axis of the first cylinder 30. The first housing portion 31communicates with the valve chamber 22.

The second cylinder 50 is fixed to a surface (an upper surface) of thefirst cylinder 30 on an opposite side to the valve main body 20. Thesecond cylinder 50 is formed of a general purpose resin, for example PP(Poly Propylene). A columnar second housing portion 54 and a columnarthird housing portion 55 are formed in an interior of the secondcylinder 50. The second housing portion 54 and the third housing portion55 communicate with each other, and respective central axes thereofmatch a central axis of the first housing portion 31. The second housingportion 54 opens onto a surface (a lower surface) of the second cylinder50, while the third housing portion 55 opens onto an opposite sidesurface (an upper surface) of the second cylinder 50. The second housingportion 54 communicates with the first housing portion 31 in the firstcylinder 30. A diameter of the second housing portion 54 is larger thana diameter of the first housing portion 31. Therefore, a step is formedbetween the first housing portion 31 and the second housing portion 54.

Respective inner walls of the second housing portion 54 and the thirdhousing portion 55 project inwardly such that an annular projectingportion 51 is formed between the second housing portion 54 and the thirdhousing portion 55. In other words, the projecting portion 51 serves asa boundary between the second housing portion 54 and the third housingportion 55.

The stepping motor 110 (the motor) is fixed to the second cylinder 50 onthe open surface (the upper surface) of the third housing portion 55with an attachment portion 113. The motor 110 includes a drive circuit112, and a signal line 132 from a controller (not shown) is connected tothe drive circuit 112. A drive control signal (a pulse signal) is inputinto the drive circuit 112 from the controller, and a rotation positionof a drive shaft 111 of the motor 110 is controlled by the drive controlsignal, which corresponds to a number of steps. Further, a photo sensor74 is provided on an outer periphery of the second cylinder 50, and asignal line 131 from the controller is connected to the photo sensor 74.The housing 120 is fixed to the surface (the upper surface) of the firstcylinder 30 on the opposite side to the valve main body 20. The secondcylinder 50, the motor 110, and the photo sensor 74 are covered by thehousing 120.

FIG. 2 is a partially enlarged view of FIG. 1. As shown in the drawing,a columnar rod 60 is housed in the first housing portion 31 and thesecond housing portion 54. The rod 60 is formed from achemical-resistant fluorine resin, for example PVDF (Poly Vinylidene DiFluoride). A columnar valve body 41 is coupled to an end portion of therod 60 on the side of the valve main body 20. A diaphragm 42 is providedon an outer peripheral edge of the valve body 41. An annular supportportion 43 is provided on an outer peripheral edge of the diaphragm 42.The support portion 43 is fixed to be sandwiched between the valve mainbody 20 and the first cylinder 30. The valve chamber 22 is separatedfrom the first housing portion 31 by the diaphragm 42 so that fluid inthe valve chamber 22 is prevented from flowing into the first housingportion 31.

The valve body 41 includes an enlarged diameter portion 41 a having alarger diameter than other parts. An annular valve seat portion 24 isformed in the valve main body 20 in a connecting portion that connectsthe flow passage 21 to the valve chamber 22. The enlarged diameterportion 41 a of the valve body 41 is disposed to face the valve seatportion 24. A wall surface of the valve seat portion 24 is parallel to awall surface of the enlarged diameter portion 41 a such that a distancebetween the respective wall surfaces remains constant.

The rod 60 (a moving member) includes a first rod portion 61 housed inthe first housing portion 31 and a second rod portion 62 housed in thesecond housing portion 54. A diameter of the second rod portion 62 islarger than a diameter of the first rod portion 61. In other words, thefirst rod portion 61 and the second rod portion 62 have dimensions thatcorrespond to the first housing portion 31 and the second housingportion 54, respectively. A central axis of the rod 60 matches thecentral axis of the valve body 41.

An annular groove portion 65 is formed in an outer peripheral surface ofthe first rod portion 61. An annular seal member 77 is fitted into thegroove portion 65 such that an inner peripheral surface of the firstcylinder 30 is sealed from the outer peripheral surface of the first rodportion 61 by the seal member 77. The first rod portion 61 slides in anaxial direction thereof while being guided by an inner peripheralsurface of the first housing portion 31. At this time, the second rodportion 62 moves in an axial direction thereof in the second housingportion 54.

A groove 52 that extends in the axial direction of the second housingportion 54 is formed in a part of an inner wall of the second housingportion 54. The groove 52 extends from the vicinity of the projectingportion 51 to a first cylinder 30 side. A pin 72 that extends in anouter diameter direction is provided in an outer peripheral edge of thesecond rod portion 62 of the rod 60. A tip end of the pin 72 is insertedinto the groove 52 to enable the second rod portion 62 to move in theaxial direction thereof while restricting rotation of the second rodportion 62 about the axis thereof.

A sensor insertion port 53 that penetrates the second cylinder 50 in aradial direction is formed in a part of the second cylinder 50 thatopposes the groove 52. A detection portion 74 a provided on a tip end ofthe photo sensor 74 is inserted into the interior of the second cylinder50 through the sensor insertion port 53. A pin 73 that extends in theouter diameter direction is provided in the outer peripheral edge of thesecond rod portion 62 of the rod 60. A tip end of the pin 73 is insertedbetween a light emitting portion and a light receiving portion of thedetection portion 74 a such that light emitted from the light emittingportion is blocked by the pin 73, and as a result, a fully open positionof the valve body 41 is detected. Note that FIGS. 1 and 2 show acondition in which the valve body 41 has been moved to a maximallyclosed side.

A cylindrical groove 63 is formed in an end surface of the second rodportion 62 on the side of the motor 110. A central axis of the groove 63matches the central axis of the second rod portion 62 (the first rodportion 61). A spring 71 (an elastic member) having a substantiallyidentical diameter to a diameter of the groove 63 is inserted into aninterior of the groove 63. One end of the spring 71 contacts a bottomportion of the groove 63, and the other end contacts the projectingportion 51. The spring 71 exerts an elastic force on the rod 60 and theprojecting portion 51 in order to move the rod 60 in a directionseparating away from the projecting portion 51, or in other words adirection for causing the valve body 41 to approach the valve seatportion 24.

A part of the second rod portion 62 that projects further toward theouter diameter side than the first rod portion 61 faces the uppersurface of the first cylinder 30. Therefore, when the rod 60 is moved inthe direction separating away from the projecting portion 51, the secondrod portion 62 impinges on the first cylinder 30 (a second restrictingportion) such that movement of the rod 60 to the valve seat portion 24side is restricted. At this time, the valve body 41 is in a condition ofmaximum closeness to the valve seat portion 24, and therefore an openingof the flow passage 21, or in other words a flow rate of the fluidflowing out through the outflow port 26, is at a minimum.

Here, a shim 75 for adjusting a position (a second restriction position)in which movement of the rod 60 to the valve seat portion 24 side isrestricted is provided between the second rod portion 62 and the firstcylinder 30. FIG. 3A is a side view of the second cylinder 50, and FIG.3B is a plan view of the shim 75.

As shown in FIG. 3A, an insertion port 56 enabling insertion of the shim75 (a spacer) from the outside is formed in the second cylinder 50. Theinsertion port 56 penetrates the second cylinder 50, and is formed in apart where the first cylinder 30 and the second cylinder 50 face eachother. As shown in FIG. 3B, the shim 75 is formed in a “U” shape, andincludes a two-pronged portion 75 a that is inserted between the firstcylinder 30 and the second rod portion 62, and an arc-shaped arc portion75 b. The shim 75 is inserted through the insertion port 56 until thearc portion 75 b impinges on the first rod portion 61 of the rod 60.Accordingly, the shim 75 can be inserted through the insertion port 56after assembling the flow rate adjustment device 10.

The position in which movement of the rod 60 to the valve seat portion24 side is restricted is adjusted by adjusting a thickness of the shim75 inserted between the second rod portion 62 and the first cylinder 30.A shim having a thickness of 0.2 mm or 0.1 mm is used either singly orin combinations of a plurality as the shim 75. In this embodiment, whenthe second rod portion 62 is pressed against the first cylinder 30 viathe shim 75, a distance (a gap) between the valve seat portion 24 andthe valve body 41 in the axial direction of the valve body 41 isadjusted to 0.2 mm. Note that the distance between the valve seatportion 24 and the valve body 41 may be adjusted appropriately inaccordance with an application of the flow rate adjustment device 10.

Returning to FIG. 2, a part of the second rod portion 62 surrounded bythe groove 63 serves as a female screw portion 64 having a female screwthread cut into an interior thereof. The female screw portion 64 isformed in a cylindrical shape to extend in the axial direction of thesecond rod portion 62. The female screw portion 64 and the spring 71(the groove 63) are provided coaxially, and therefore a space fordisposing the female screw portion 64 and the spring 71 in the axialdirection of the rod 60 can be reduced.

The drive shaft 111 of the motor 110 is inserted into the third housingportion 55. The drive shaft 111 is provided with a first engagementportion 90. A second engagement portion 80 that engages with the firstengagement portion 90 is housed in the third housing portion 55 and thesecond housing portion 54. The first engagement portion 90 and thesecond engagement portion 80 are formed of a material capable oftransmitting driving force from the motor 110, for example stainlesssteel.

FIG. 4 is an exploded perspective view showing the first engagementportion 90 and the second engagement portion 80. As shown in thedrawing, the second engagement portion 80 includes a male screw portion82 into which a male screw thread is cut, and a head portion 81 having alarger diameter than the male screw portion 82. The second engagementportion 80 has an overall shape that resembles a slotted screw, and themale screw portion 82 extends in an axial direction thereof. A grooveportion 83 (a recessed portion) that extends in a radial direction isformed in the head portion 81. A width and a depth of the groove portion83 are constant, and the depth of the groove portion 83 is substantiallyequal to a thickness of the head portion 81. Two inside surfaces 80 a ofthe groove portion 83 are parallel to each other and equidistant from acentral axis of the head portion 81. The central axis of the headportion 81 matches a central axis of the male screw portion 82.

The first engagement portion 90 (an insertion portion), which isinserted into the groove portion 83 of the second engagement portion 80,is provided on the drive shaft 111 of the motor 110. The firstengagement portion 90 is formed in a rectangular parallelepiped shape,and a central portion of the first engagement portion 90 in a lengthwisedirection thereof is fixed to the drive shaft 111. The first engagementportion 90 includes mutually parallel outside surfaces 90 a. A thicknessof the outside surface 90 a in an axial direction of the drive shaft 111is set to be thinner than the thickness of the head portion 81 of thesecond engagement portion 80.

A lengthwise direction length of the first engagement portion 90 issubstantially equal to a diameter of the head portion 81 of the secondengagement portion 80. A width of the first engagement portion 90 isslightly narrower than the width of the groove portion 83 in the secondengagement portion 80. The first engagement portion 90 is inserted intothe groove portion 83 in the central axis direction while the centralaxis of the drive shaft 111 of the motor 110 is aligned with the centralaxis of the second engagement portion 80. As a result, the outsidesurfaces 90 a of the first engagement portion 90 and the inside surfaces80 a of the groove portion 83 are fitted together with a gaptherebetween.

Returning to FIG. 2, the first engagement portion 90 and the secondengagement portion 80 are capable of moving relative to each other inthe axial direction of the drive shaft 111 and capable of transmittingrotary force to each other. The male screw portion 82 of the secondengagement portion 80 meshes with the female screw portion 64 of thesecond rod portion 62 (the rod 60). The rod 60 is pushed toward thevalve seat portion 24 by the spring 71. The second engagement portion 80is coupled to the rod 60 via the male screw portion 82 and the femalescrew portion 64. Accordingly, the second engagement portion 80 ispulled toward the valve seat portion 24 by the rod 60. When the secondengagement portion 80 is moved toward the valve seat portion 24, thehead portion 81 of the second engagement portion 80 impinges on theprojecting portion 51 (the first restricting portion) such that movementof the second engagement portion 80 to the valve seat portion 24 side isrestricted.

A thrust washer 76 that receives a force acting in the axial directionof the second engagement portion 80 is provided between the secondengagement portion 80 and the projecting portion 51. Hence, when thesecond engagement portion 80 rotates about the male screw portion 82,the head portion 81 and the thrust washer 76 slide smoothly. Further, aforce for pulling the second engagement portion 80 toward the valve seatportion 24 is received by the projecting portion 51 and the thrustwasher 76. The position in which movement of the second engagementportion 80 is restricted corresponds to a first restriction position.

The respective central axes of the valve body 41, the rod 60, the secondengagement portion 80, and the drive shaft 111 all match. The male screwportion 82 of the second engagement portion 80 and the female screwportion 64 of the rod 60 are fed relative to each other in the axialdirection of the drive shaft 111 when rotated relative to each other. Inother words, when the second engagement portion 80 is rotated by thedrive shaft 111 via the first engagement portion 90, the distancebetween the head portion 81 of the second engagement portion 80 and thesecond rod portion 62 of the rod 60 is modified. FIG. 2 shows acondition in which a rotation position (a step number) of the driveshaft 111 of the motor 110 corresponds to a reference position (areference step number). In this condition, the second rod portion 62 ofthe rod 60 impinges on the shim 75 and the head portion 81 of the secondengagement portion 80 impinges on the thrust washer 76. Meanwhile, a gap(a space) is formed between a bottom portion of the first engagementportion 90 and a bottom portion of the groove portion 83 in the secondengagement portion 80.

Next, referring to FIG. 5, an operation performed in the flow rateadjustment device 10 to increase the opening of the flow passage 21using the valve body 41 will be described. Driving of the drive shaft111 of the stepping motor 110 is controlled by the aforementionedcontroller.

When the drive shaft 111 is rotated in the direction of an arrow in thedrawing, rotary force is transmitted from the first engagement portion90 to the second engagement portion 80. The second engagement portion 80is pulled toward the valve seat portion 24 by the elastic force of thespring 71, and movement of the second engagement portion 80 isrestricted by the thrust washer 76 and the projecting portion 51.Further, rotation of the rod 60 in a rotary direction of the drive shaft111 is restricted by the pin 72 inserted into the groove 52 in thesecond cylinder 50.

Hence, by rotating the male screw portion 82 of the second engagementportion 80, the female screw portion 64 is fed in a directionapproaching the drive shaft 111 such that the head portion 81 of thesecond engagement portion 80 and the second rod portion 62 of the rod 60approach each other. Accordingly, the rod 60 is moved in the directionof an arrow in the drawing, and in accompaniment therewith, the valvebody 41 moves in a direction separating away from the valve seat portion24. As a result, the distance between the valve seat portion 24 and thevalve body 41, or in other words the opening of the flow passage 21, isadjusted such that the flow rate of the fluid flowing out into the flowpassage 23 is adjusted.

Here, the first engagement portion 90 and the second engagement portion80 are capable of relative movement in the axial direction of the driveshaft 111. Therefore, when the rod 60 is fed in the axial direction, areaction to a force thereof can be prevented from acting on the driveshaft 111 in the axial direction. Further, the rotation position of thedrive shaft 111 is controlled precisely on the basis of the step numberof the motor 110, and therefore the opening of the flow passage 21 canbe controlled precisely.

When the rod 60 is moved further such that the pin 73 is detected by thedetection portion 74 a of the photo sensor 74, it is determined that thevalve body 41 has reached the fully open position, and rotation of thedrive shaft 111 is stopped. At this time, a gap is formed between thesecond rod portion 62 of the rod 60 and the projecting portion 51. Inother words, the rod 60 can be moved in the direction of the arrow inthe drawing until the second rod portion 62 impinges on the projectingportion 51, but when the fully open position of the valve body 41 isdetected by the detection portion 74 a, further movement of the rod 60is prohibited. Thus, the rod 60 can be prevented from impinging on theprojecting portion 51, and as a result, an excessive load can beprevented from acting on the motor 110.

Referring to FIG. 6, an operation performed in the flow rate adjustmentdevice 10 to reduce the opening of the flow passage 21 using the valvebody 41 will be described. Driving of the drive shaft 111 of thestepping motor 110 is controlled by the aforementioned controller.

When the drive shaft 111 is rotated in the direction of an arrow in thedrawing (an opposite direction to that of FIG. 5), rotary force istransmitted from the first engagement portion 90 to the secondengagement portion 80. In this case, when the male screw portion 82 ofthe second engagement portion 80 is rotated, the female screw portion 64is fed in a direction approaching the valve seat portion 24 such thatthe head portion 81 of the second engagement portion 80 heads away fromthe second rod portion 62 of the rod 60. Accordingly, the rod 60 ismoved in the direction of an arrow in the drawing (an opposite directionto that of FIG. 5), and in accompaniment therewith, the valve body 41moves in a direction approaching the valve seat portion 24. As a result,the distance between the valve seat portion 24 and the valve body 41, orin other words the opening of the flow passage 21, is adjusted such thatthe flow rate of the fluid flowing out into the flow passage 23 isadjusted.

When the second rod portion 62 of the rod 60 impinges on the shim 75such that movement of the rod 60 is restricted by the shim 75 and thefirst cylinder 30, the valve seat 41 is in the condition of maximumcloseness to the valve seat portion 24. When the drive shaft 111 isrotated further from this condition, the head portion 81 of the secondengagement portion 80 and the second rod portion 62 of the rod 60 arefed relative to each other in a direction separating away from eachother. Here, the first engagement portion 90 and the second engagementportion 80 are capable of relative movement in the axial direction ofthe drive shaft 111, while movement of the rod 60 in the directiontoward the valve seat portion 24 is restricted. Hence, when the driveshaft 111 and the second engagement portion 80 are rotated, the secondengagement portion 80 is moved in a direction that causes the headportion 81 to head away from the thrust washer 76 and the projectingportion 51, or in other words the direction of an arrow in the drawing.

Hence, even when movement of the rod 60 is restricted and the valve body41 is in the condition of maximum closeness to the valve seat portion24, rotation of the second engagement portion 80 and the drive shaft 111is not restricted. Therefore, an excessive load can be prevented fromacting on the motor 110, and as a result, the motor 110 can be preventedfrom losing steps. Here, a space is provided between the bottom portionof the first engagement portion 90 and the bottom portion of the grooveportion 83, and therefore the second engagement portion 80 can beallowed to move away sufficiently in the direction toward the motor 110even when the drive shaft 111 is rotated while movement of the rod 60 isrestricted.

The second engagement portion 80 can be exposed by detaching the housing120 and the motor 110 from the flow rate adjustment device 10. In sodoing, the second engagement portion 80 can be rotated easily by hand,whereby the position of the valve body 41 can be adjusted manually. As aresult, a maintainability of the flow rate adjustment device 10 can beimproved.

The embodiment described in detail above exhibits following advantages.

The first engagement portion 90 and the second engagement portion 80 arecapable of relative movement in the axial direction of the drive shaft111. Therefore, by rotating the second engagement portion 80 whenmovement of the rod 60 is restricted, the head portion 81 of the secondengagement portion 80 is fed in the direction separating away from thesecond rod portion 62 of the rod 60, or in other words a directionseparating away from the projecting portion 51. Hence, an excessive loadcan be prevented from acting on the motor 110 even when the motor 110 isdriven further from a condition in which movement of the rod 60 isrestricted. As a result, the motor 110 can be prevented from losingsteps, and the precision with which the position of the valve body 41 isadjusted can be prevented from decreasing. Further, damage to the motor110 or the like can be suppressed.

Furthermore, the first engagement portion 90 and the second engagementportion 80 are capable of transmitting rotary force to each other andcapable of moving relative to each other in the axial direction of thedrive shaft 111. Therefore, a reaction to the force for feeding the rod60 in the axial direction and a reaction to the force for feeding thehead portion 81 of the second engagement portion 80 in the directionseparating away from the projecting portion 51 can be prevented fromacting on the drive shaft 111 of the motor 110 in the axial direction.As a result, an increase in a rotary load of the motor 110 can besuppressed, whereby a reduction in a durability of the motor 110 and anincrease in a size of the motor 110 can be suppressed.

The second restriction position is adjusted by the shim 75 in an uppersurface portion of the first cylinder 30, where movement of the rod 60to the valve seat portion 24 side beyond the second restriction positionis restricted. Therefore, the gap between the valve seat portion 24 andthe valve body 41, or in other words a flow condition of the fluid, inthe condition of maximum closeness between the valve body 41 and thevalve seat portion 24, can be controlled precisely. Further, in acondition where movement of the rod 60 is restricted by the uppersurface portion of the first cylinder 30, a gap is formed between thevalve seat portion 24 and the valve body 41, and therefore the valvebody 41 can be prevented from impinging on the valve seat portion 24. Asa result, situations in which the valve body 41 is pressed forcefullyagainst the valve seat portion 24, particles are generated from thevalve body 41 and the valve seat portion 24, and the valve body 41 andthe valve seat portion 24 are deformed or damaged can be suppressedeffectively.

Movement of the rod 60 in the axial direction is guided by the firstcylinder 30 and the second cylinder 50. Further, the shim 75 can beinserted through the insertion port 56 from the outside of the firstcylinder 30. Therefore, the gap between the valve seat portion 24 andthe valve body 41 can be adjusted finely by the shim 75 after assemblingthe flow rate adjustment device 10. Hence, a high degree of dimensionalprecision is not required in the valve main body 20, the first cylinder30, the rod 60 or the like, and as a result, fluid control precision canbe maintained while suppressing costs.

The rectangular parallelepiped-shaped insertion portion of the firstengagement portion 90 can be inserted into the groove portion 83 of thesecond engagement portion 80 in the axial direction of the drive shaft111. Further, the mutually parallel outside surfaces 90 a of the firstengagement portion 90 and the inside surfaces 80 a of the groove portion83 are fitted together with a gap therebetween. Hence, functions of thefirst engagement portion 90 and the second engagement portion 80 can berealized by a simple configuration.

The present invention is not limited to the above embodiment, and may beembodied as follows, for example.

In the above embodiment, the insertion portion is provided in the firstengagement portion 90 and the groove portion 83 (the recessed portion)is formed in the second engagement portion 80. However, a groove portion(a recess portion) may be formed in the first engagement portion 90 andan insertion portion may be provided in the second engagement portion80.

Further, as long as the first engagement portion 90 and the secondengagement portion 80 are capable of moving relative to each other inthe axial direction of the drive shaft 111 of the motor 110 andtransmitting rotary force to each other, their shapes may be modified asdesired.

In the above embodiment, the male screw portion 82 is provided on thesecond engagement portion 80 and the female screw portion 64 is providedin the rod 60. However, a female screw portion may be provided in thesecond engagement portion 80 and a male screw portion may be provided onthe rod 60.

A configuration in which the valve body 41 contacts the valve seatportion 24 when the valve body 41 is in the condition of maximumcloseness to the valve seat portion 24 may be employed. With thisconfiguration, by allowing the second engagement portion 80 to move awayin the direction toward the motor 110, situations in which the valvebody 41 is pressed forcefully against the valve seat portion 24 and anexcessive load is exerted on the motor 110 can be suppressed.

Instead of the spring 71, an elastic member made of a rubber material orthe like, a configuration using repulsive force generated by a magnet,or the like may be employed.

A motor other than the stepping motor 110, for example a servo motor ora DC motor, may be employed.

The present invention is not limited to the flow rate adjustment device10, and may be realized as a pressure adjustment device that adjusts afluid pressure. Further, the fluid is not limited to a liquid, and a gasmay be used instead.

What is claimed is:
 1. A fluid control device comprising: a motor havinga drive shaft; a first engagement portion provided on the drive shaft; asecond engagement portion configured to move relative to the firstengagement portion in an axial direction of the drive shaft and receivea rotary force from the first engagement portion; a valve main bodyhaving a flow passage for a fluid and a valve seat portion; a valve bodyprovided to face the valve seat portion in order to adjust an opening ofthe flow passage; a moving member coupled to the valve body of whichmovement in the axial direction is permitted and of which rotation aboutthe drive shaft is restricted; an elastic member configured to exert aforce on the moving member in a direction for causing the valve body toapproach the valve seat portion; a first restricting portion configuredto restrict movement of the second engagement portion to the side of thevalve seat portion beyond a first restriction position; and a secondrestricting portion configured to restrict movement of the moving memberto the side of the valve seat portion beyond a second restrictingposition, wherein the second engagement portion and the moving memberare screwed together such that the second engagement portion and themoving member move relative to each other in the axial direction whenrotated relative to each other.
 2. The fluid control device according toclaim 1, wherein the second restricting portion is provided with aspacer for adjusting the second restriction position, and in a conditionwhere movement of the moving member is restricted by the secondrestricting portion, a gap is formed between the valve seat portion andthe valve body.
 3. The fluid control device according to claim 2,further comprising a cylinder configured to guide movement of the movingmember in the axial direction, wherein an insertion port into which thespacer is inserted from outside is formed in the cylinder.
 4. The fluidcontrol device according to claim 1, wherein one of the first engagementportion and the second engagement portion includes a rectangularparallelepiped-shaped insertion portion, the other of the firstengagement portion and the second engagement portion includes a recessedportion into which the insertion portion is inserted in the axialdirection, and outside surfaces of the insertion portion and insidesurfaces of the recessed portion are mutually parallel and fittedtogether with a gap between the surfaces.
 5. The fluid control deviceaccording to claim 1, wherein the motor is a stepping motor configuredto rotate in synchronization with pulse power.
 6. The fluid controldevice according to claim 2, wherein one of the first engagement portionand the second engagement portion includes a rectangularparallelepiped-shaped insertion portion, the other of the firstengagement portion and the second engagement portion includes a recessedportion into which the insertion portion is inserted in the axialdirection, and outside surfaces of the insertion portion and insidesurfaces of the recessed portion are mutually parallel and fittedtogether with a gap between the surfaces.
 7. The fluid control deviceaccording to claim 3, wherein one of the first engagement portion andthe second engagement portion includes a rectangularparallelepiped-shaped insertion portion, the other of the firstengagement portion and the second engagement portion includes a recessedportion into which the insertion portion is inserted in the axialdirection, and outside surfaces of the insertion portion and insidesurfaces of the recessed portion are mutually parallel and fittedtogether with a gap between the surfaces.
 8. The fluid control deviceaccording to claim 2, wherein the motor is a stepping motor configuredto rotate in synchronization with pulse power.
 9. The fluid controldevice according to claim 3, wherein the motor is a stepping motorconfigured to rotate in synchronization with pulse power.
 10. The fluidcontrol device according to claim 4, wherein the motor is a steppingmotor configured to rotate in synchronization with pulse power.